Molecular cloning of a DNA fragment from human chromosome 14(14q11) involved in T-cell malignancies

β-Catenin induces T-cell transformation by promoting genomic instability

Deregulated activation of β-catenin in cancer has been correlated with genomic instability. During thymocyte development, β-catenin activates transcription in partnership with T-cell-specific transcription factor 1 (Tcf-1). We previously reported that targeted activation of β-catenin in thymocytes (CAT mice) induces lymphomas that depend on recombination activating gene (RAG) and myelocytomatosis oncogene (Myc) activities. Here we show that these lymphomas have recurring Tcra/Myc translocations that resulted from illegitimate RAG recombination events and resembled oncogenic translocations previously described in human T-ALL. We therefore used the CAT animal model to obtain mechanistic insights into the transformation process. ChIP-seq analysis uncovered a link between Tcf-1 and RAG2 showing that the two proteins shared binding sites marked by trimethylated histone-3 lysine-4 (H3K4me3) throughout the genome, including near the translocation sites. Pretransformed CAT thymocytes had increased DNA damage at the translocating loci and showed altered repair of RAG-induced DNA double strand breaks. These cells were able to survive despite DNA damage because activated β-catenin promoted an antiapoptosis gene expression profile. Thus, activated β-catenin promotes genomic instability that leads to T-cell lymphomas as a consequence of altered double strand break repair and increased survival of thymocytes with damaged DNA.

What retroviruses teach us about the involvement of c-Myc in leukemias and lymphomas

Overexpression of the cellular oncogene c-Myc frequently occurs during induction of leukemias and lymphomas in many species. Retroviruses have enhanced our understanding of the role of c-Myc in such tumors. Leukemias and lymphomas induced by retroviruses activate c-Myc by: (1) use of virally specified proteins that increase c-Myc transcription, (2) transduction and modification of c-Myc to generate a virally encoded form of the gene, v-Myc, and (3) proviral integration in or near c-Myc. Proviral integrations elevate transcription by insertion of retroviral enhancers found in the long terminal repeat (LTR). Studies of the LTR enhancer elements from these retroviruses have revealed the importance of these elements for c-Mycactivation in several cell types. Retroviruses also have been used to identify genes that collaborate with c-Myc during development and progression of leukemias and lymphomas. In these experiments, animals that are transgenic for c-Mycoverexpression (often in combination with the overexpression or deletion of known proto-oncogenes) have been infected with retroviruses that then insertionally activate novel co-operating cellular genes. The retrovirus then acts as a molecular 'tag' for cloning of these genes. This review covers several aspects of c-Myc involvement in retrovirally induced leukemias and lymphomas.

Molecular analysis of the t(8;14)(q24;q11) chromosomal breakpoint junctions in the T-cell leukemia line MOLT-16

The MOLT-16 cell line was established from the leukemic cells of a patient with T-cell acute lymphoblastic leukemia and contains a t(8;14)(q24;q11) resulting in juxtaposition of sequences downstream of the MYC gene on chromosome 8 and the J region of the T-cell receptor alpha chain gene (TCRA) on chromosome 14. The reciprocal translocation involved a complex rearrangement with two chromosome breakpoints within the TCRAJ region on chromosome 14, resulting in inversion of a 1.4 kb DNA fragment between the two breakpoints. The 5' border of the inversion joints with another segment of chromosome 14, whereas the 3' border joins with a region of chromosome 8 located at least 257 kb downstream of MYC. Extensive deletions have occurred on both chromosomes 8 and 14 in conjunction with the translocation. To investigate the possible involvement of the V(D)J recombinase in this translocation, we analyzed the nucleotide sequences surrounding the translocation breakpoints. The breakpoint on chromosome 14 occurs between a segment coding for a TCRAJ sequence and its hepatamer-nonamer signal. Heptamer-nonamer consensus sequences are also identified on chromosome 8 adjacent to the breakpoint. Inserted N and P nucleotides are observed at the breakpoint junctions.

t(11;18)(q21;q21) may delineate a spectrum of diffuse small B-cell lymphoma with extranodal involvement

We describe a patient with stage IV non-Hodgkin's lymphoma (NHL) and a t(11;18)(q21;q21) translocation. He presented with a gastric small B-cell lymphocytic lymphoma, expressing IgAL immunoglobulins without expression of CD10, CD5, and CD23 antigens. The lymphoma was the final development of a 6-year history of a monoclonal IgAL increase complicated by severe renal failure due to membranoproliferative glomerulonephritis. The clinical, histological, immunologic, and cytogenetic features of this patient are very similar to those observed in the five other patients with t(11;18) reported to date. This translocation therefore seems to delineate a new subtype of diffuse small B-cell lymphoma with involvement of mucosal sites. Involvement of the BCL2 oncogene on 18q21 could not be detected using molecular techniques with 5' as well as 3' BCL2 probes, indicating that other, so far unknown, genes relevant to lymphoid differentiation could be located in 18q21 and 11q21.

Molecular analysis of a variant 18;22 translocation in a case of lymphocytic lymphoma

We previously reported a 5' rearrangement of the BCL2 locus in a t(18;22) variant translocation found in a lymphocytic lymphoma. Primary structure analysis of both rearranged chromosomes confirmed the localization of the breakpoint in the so-called vcr region (for variant cluster region) that encompasses Z-DNA stretches 5' of the BCL2 locus, and in between J lambda 1 and C lambda 1 segments on the IGL locus. A 1,027 nucleotide segment from chromosome 22 was repeated on both derivative chromosomes 18q+ and 22q-. This segment contained an octanucleotide that was also present in the normal chromosome 18 close to the breakpoint. As a consequence of the translocation, a normal-sized BCL2 transcript was overexpressed in tumor cells.

Chromosomal localization of HTLV-1 viral integration sites using in situ hybridization: detection of a novel IL2R fragment

The presence of human T-cell leukemia virus (HTLV-1) in patients with adult T-cell leukemia (ATL) was investigated by Southern blotting and in situ hybridization. In all seven patients, HTLV-1 provirus was detected. A large and variable number of labeled restriction fragments were observed, indicating multiple integrations. Two of the patients analyzed by in situ hybridization had two, while the third patient had three, sites of viral integration on six different chromosomes, suggesting random integration. A single site of integration was shared by two patients, which was on chromosome 10 at bands p11-->p15. One of these sites was on an apparently normal chromosome 10 and the other was on a derivative chromosome 10,t(10;14)(p12;q32). The interleukin 2 receptor (IL2R) has previously been localized to this region (10p14-->p15). The alpha-chain of the IL2R is continuously expressed on affected T-cells in this disease. Southern blotting with pIL2R showed the presence of a novel 3.5 kb fragment in five out of the seven patients. This novel fragment has not been previously reported. No direct correlation was found between the novel 3.5 kb fragment, present in patients both cytogenetically normal and abnormal, and viral integration in the 10p11-->p15 region in two patients. Therefore, it is suggested that the presence of the 3.5 kb fragment and the numerous chromosomal breaks associated with this disease may not be direct results of viral integration.

t(18;22)(q21;q11) with rearrangement of BCL2 as a possible secondary change in a lymphocytic lymphoma

We report a lymphocytic lymphoma showing a combination of two characteristic neoplasia-associated chromosomal changes: trisomy 12, commonly observed in chronic lymphocytic leukemia and lymphocytic lymphoma, and t(18;22)(q21;q11), a variant form of the t(14;18)(q32;q21) found in most follicular lymphomas. Southern blot analysis was performed using probes for the 5' end of the BCL2 gene (18q21) and for the J lambda as well as C lambda immunoglobulin genes (22q11). With these two probes, a unique rearranged fragment was detected. Thus the t(18;22)(q21;q11) can be considered as a variant translocation of t(14;18)(q32;q21). The karyotypic analysis supports the assumption that in our case trisomy 12 occurred first, and t(18;22) appeared during tumor progression as part of the clonal evolution. This is at variance with the typical t(14;18), which has never been found to occur as a secondary change.

Cytogenetic implication in adult T-cell leukemia. A hypothesis of leukemogenesis

The close association between adult T-cell leukemia (ATL) and human T-cell leukemia virus type I (HTLV-I) has been established. Nevertheless, the mechanism of progression of ATL by HTLV-I infection is still uncertain, because the virus contains no typical oncogene and no significant expression of the viral RNA has been generally found. I propose a model of leukemogenic process in ATL based on our cytogenetic data and molecular results in the literature. It seems that the rearrangement of some proto-oncogene and alpha-chain gene of the T-cell antigen receptor (TCR-alpha) is necessary for the development to overt ATL. A deficiency in the rearrangement of proto-oncogene to TCR-alpha may result in only a minor proliferation of abnormal lymphocytes and remain in the preleukemic state of ATL or in the HTLV-I carrier state.

Molecular analysis of the t(1;19) breakpoint cluster region in pre-B cell acute lymphoblastic leukemias

The t(1;19) chromosomal translocation in acute lymphoblastic pre-B cell leukemias involves the gene E2A for helix-loop-helix (HLH) proteins E12 and E47, ubiquitous transcriptional proteins implicated in the regulation of various lymphoid and nonlymphoid genes. To characterize the molecular features of the t(1;19)(q23;p13) translocation, we molecularly cloned breakpoint DNA from t(1;19)-carrying pre-B cell leukemias. In all cases, breakpoints on chromosome 19 occurred within 2 kb of each other in a single intron of the E2A gene. This clustered arrangement resulted in specific truncation of the E2A gene and transcript, with loss of sequences encoding the basic DNA-binding and HLH dimerization motifs from the derivative 19 chromosome. In contrast, breakpoints on chromosome 1 were distributed over a large region and could not be linked to exonic sequences of the PBX1 gene, although identical chromosome 1 sequences are joined to E2A sequences in 1;19 fusion transcripts. These data show that the 1;19 translocation consistently results in exchange of 3' exons encoding the HLH motifs of E2A with DNA from chromosome 1 to form a fusion gene on the derivative 19 chromosome.

Malignant histiocytosis. A phenotypic and genotypic investigation

Ten cases of malignant histiocytosis (MH) were evaluated for clinical and histopathologic features, phenotype, and rearrangement of T cell receptor (TCR) beta, gamma, and alpha and immunoglobulin (Ig) genes (7/10). All cases were HLA-DR+ and CD30-positive. Four cases had molecular evidence of T cell lineage such as TCR beta, gamma, and alpha rearrangements, and one additional case synthesized the cytoplasmic TCR beta chain. The remaining five cases did not show unequivocal T, B, natural killer (NK) cell, or macrophagic origin, and three of them had germline TCR and Ig genes. Ultrastructural analysis was not helpful for the definition of the cell lineage. Most myelomonocytic markers (MAC387, CD13, CD14, CD64, CD68) were either negative on the MH cells or were expressed on cells with rearranged TCR gene. Precursor (CD34, CD7) and NK (CD16, CD56, and CD57) cell markers were not found. The lineage of a number of cases of MH remains unresolved.

Two distinct mechanisms for the SCL gene activation in the t(1;14) translocation of T-cell leukemias

Molecular study of a t(1;14)(p32;q11) translocation found in an acute T-cell leukemia (Kd cells) with a relatively mature phenotype is reported. Complex DNA rearrangements were characterized in the TCR alpha/delta locus. Besides a productive V alpha/J alpha assembly found on the normal allele, two deletions within the J alpha cluster were identified in the translocated allele. The translocation breakpoints involved the TCR delta gene on chromosome 14 and the SCL locus on chromosome band Ip32 that was recently shown to be activated by the t(1;14) translocation of the DU 528 leukemic cell line. Significantly, both Kd and DU 528 translocation breakpoints were located at the boundaries of D delta or J delta segments and were clustered in a 10 kb genomic fragment of the SCL gene. The presence of recombination signal motifs (heptamer-12/23 bp spacer-nonamer) on both normal chromosome partners, and N nucleotide addition on both derivative chromosomes involved the recombinase system in the translocation event. The SCL locus was highly expressed as a 5 kb transcript in Kd cells and, as already reported, as a 2 kb transcript in DU 528 cells. Importantly, a 5 kb SCL transcript was also detected in immature nonlymphoid hematopoietic cells but not in normal mature T cells, suggesting that it might correspond to the normal SCL transcript. Taken together, our data support the notion that the involvement of the SCL gene in the leukemogenic process may occur through overexpression of an apparently normal transcript (Kd cells) or expression of a truncated RNA (DU 528 cells).

Topoisomerase II-mediated DNA cleavage activity induced by ellipticines on the human tumor cell line N417

Ellipticine derivatives have been shown to induce DNA strand breaks by trapping DNA-topoisomerase II (Topo II) in an intermediary covalent complex between Topo II and DNA which could be related to their cytotoxic effects. We report here that Celiptium and Detalliptinium, two ellipticine derivatives clinically used for their antitumoral properties against breast cancer, exhibit the highest in vitro activity on Topo II DNA cleavage reaction and decatenation among a series of 14 ellipticine derivatives. The in vitro cleavage site specificity in pBR 322 plasmid DNA and in a human c-myc gene inserted in a lambda phage DNA is identical for both ellipticines, but different from m-AMSA, another Topo II related antitumoral agent. Recently, it has been shown that the ellipticine derivative Celiptium presents a strong cytotoxic activity in vitro on different human tumors including small cell lung carcinoma (SCLC). However, the studies that involved Topo II as a target for ellipticine derivatives have been performed only by using animal tumor cell lines. Therefore we have studied the in vivo DNA cleavage activity of Celiptium and Detalliptinium on a human SCLC cell line, NCI N417, comparatively to that obtained with m-AMSA. The respective IC50 on cell growth are 9, 8 and 1 microM for Celiptium, Detalliptinium and m-AMSA, respectively. Using the alkaline elution technique, we have observed that Celiptium and Detalliptinium exhibit a weak cleavage activity on genomic DNA from whole cells. The ellipticines are about 50 times less potent than m-AMSA in inducing DNA strand breaks. Analysis of in vivo c-myc gene cleavage by Southern blot hybridization also demonstrates a lack of activity of the ellipticine derivatives as no gene cleavage could be detected up to 50 microM of the drug. With m-AMSA, c-myc gene cleavage is detected at a concentration of 0.2 microM, which indicates that this methodology is less sensitive in detecting DNA strand breaks than is the alkaline elution. Further studies of the drug effect on isolated nuclei by alkaline elution also show that the DNA cleavage activity of Celiptium and Detalliptinium is increased when compared to whole cells. Our data indicate that these two drugs have a weaker cytotoxic effect than m-AMSA on NCI N417 cell line, due to a limited access to the cell nucleus rather than to a lack of activity on Topo II as assessed by in vitro and isolated nuclei experiments.

An analysis in human lymphomas of a J alpha region involved in a c-myc/J alpha translocation; relationship with TCR alpha, beta, and gamma rearrangements

The D14S7 locus defines the breakpoint on chromosome 14 of a t (8;14) (q24;q11) present in the T-cell line KE37-R in which DI4S7 sequences translocate 3' to the c-myc oncogene. It has been shown previously that DI4S7 rearranges specifically in some but not all T cell clones and in the present study we investigated the frequency and specificity of its rearrangements in human fresh lymphoma samples. DI4S7 rearrangements were extremely specific since they were detected in 3 out of 5 T-cell lymphoma samples positive for TCR beta and gamma but not in 17 miscellaneous non-T lymphomas, 4 non neoplastic lymphnodes as well as unstimulated and activated polyclonal T-cells. Most of the rearrangements were in the form of deletions that appear to involve large pieces of DNA since the segments detected by a V alpha probe were also deleted. Rearrangement of DI4S7 and V alpha regions were detected in lymphomas with a cortical thymocyte phenotype, demonstrating that they appear quite early in the differentiation of T cells.

Structure and rearrangement of the T cell receptor J alpha locus in T cells and leukemic T cell lines

The vast majority of T cells express an antigen receptor (TcR) composed of an alpha/beta heterodimer. The alpha and beta chains are encoded for by a set of variable (V), joining (J) and constant (C) region genes. Unlike the J genes of the beta chain which are limited in number and are clustered close to the constant region, the J alpha genes are spread over an 85-kilobase DNA region, upstream of the C alpha gene. We have isolated the complete J alpha locus, bounded on the 5' side by the C sequence of the delta gene and on the 3' side by the C sequence of the alpha gene. The experiments described here demonstrate that the J gene segments extend 75 kb 5' of C alpha and participate equally in generating the diversity of the alpha chain in peripheral T cells. Similarly, in leukemic T cell lines, rearrangements occurred over the entire locus and involved both alleles. Densitometry data suggest that in most peripheral T cells both alleles also are rearranged; thus, allelic exclusion in the alpha locus does not occur at the level of rearrangement. In three cell lines, an identical rearrangement has occurred on one allele in a region located 10 kb from the 5' end of the locus.

Specific abnormalities of chromosome 14 in patients with acute type of adult T-cell leukemia/lymphoma

Chromosome analysis was performed on 1 patient with diffuse lymphoma of mixed type by histologic diagnosis and on 7 patients with the acute type of adult T-cell leukemia (ATL). Specific abnormalities in chromosome 14 at break band q11 with the assigned locus of the alpha-chain gene of the T-cell antigen receptor were identified in 6 of 8 patients. Inv(14) (q11q32) was found in 2 patients and translocation of chromosome 14 at break band q11 was observed in 4. Donor chromosomes involved in translocation of the 14q11 varied, i.e., chromosomes 3, 7 or X, with the exception of one patient whose donor chromosome origin could not be determined. The breakpoint in chromosome 3 was in band p25, a region reported to include the locus of the c-raf-I oncogene. In chromosome 7, it was in band p11, a region reported to include the locus of the c-erb-B oncogene, and in the sex chromosome X, it was in band q11. One patient also had a chromosome 14 aberration at break band q32. Of the 2 remaining patients, one had lost chromosome 14 and the other had an isochromosome 14q. Our observation and other reported findings suggest that the rearrangement of chromosome 14 at break band q11 is specific for lymphoma-type or acute-type ATL patients, and aberrations of proto-oncogene expression or the coding sequence by recombination involving a T-cell antigen receptor gene due to chromosome inversion or chromosome translocation may play an important role in T-cell neoplasia including ATL.

Cytogenetic studies of Sézary cells

Cytogenetic studies of two patients with Sézary's syndrome and of one patient with mycosis fungoides are reported. One chromosome #14 at band 14q11 was involved in chromosomal rearrangements in one patient. A review of previously reported cases shows that some chromosome abnormalities appeared nonrandomly, involving chromosomes #1, #4, #6, #7, #9, #13, #14, and #17. Abnormalities on 2p and monosomy 10 were emphasized.

Monoclonality in human T-cell disorders

The genes coding for the T-cell antigen receptor have recently been cloned. They have proven to be invaluable tools for the study of the molecular mechanisms governing T-cell recognition of foreign antigens associated with histocompatibility antigens. In addition, they have also provided sensitive means of detecting clonal cell populations and determining cell lineage. In this review we describe the general organisation of these genes, the results of their utilization in the analysis of hematological pathologies, and discuss the possible implications of the involvement of these genes in translocations observed in certain T-cell malignancies.

A t(8;14)(q24;q11) translocation in a T-cell leukemia (L1-ALL) with c-myc and TcR-alpha chain locus rearrangements

Cell lines established from T-cell leukemias have recently been reported to exhibit a chromosome translocation t(8;14) involving proto-oncogene c-myc and the gene of the T-cell receptor alpha-chain(TcR-alpha). In this work, we have studied a case of T-cell leukemia presenting a t(8;14)(q24;q11) translocation that was found in fresh leukemic cells taken during relapse, but was absent in cells collected at diagnosis. Hybridization analysis showed that the breakpoint on chromosome 8 was located 3' to the c-myc exon 3. A TcR-alpha-specific original probe (D14S7, Mathieu-Mahul et al., 1985) revealed two differently rearranged patterns in DNA from leukemic cells obtained at diagnosis and during relapse. In contrast, the rearranged TcR-beta-gene DNA pattern did not change during the course of the disease, indicating that leukemic cells were clonally related. These data indicate that the chromosome breakpoint in 14q11 is situated in the TcR-alpha locus. These results suggest that translocations t(8;14) involving TcR-alpha and c-myc genes in T-cell malignancies are analogous to variant t(2;8) and t(8;22) translocations observed in Burkitt lymphoma. They also establish that the same types of molecular rearrangements due to a t(8;14)(q24;q11) translocation, at first described in T-cell lines established in culture, also exist in vivo and may play a role in the evolution of the leukemic process.

Characterization of the topoisomerase II-induced cleavage sites in the c-myc proto-oncogene. In vitro stimulation by the antitumoral intercalating drug mAMSA

In an attempt to get an insight into the activity of mAMSA (a DNA topoisomerase II-mediated drug) on the human proto-oncogene c-myc, an in vitro system consisting of purified calf thymus DNA topoisomerase II and a c-myc DNA inserted in lambda phage was utilized. The occurrence of discrete bands, detected by hybridization of Southern blots with appropriate c-myc probes, indicated the presence of cleavage sites in the sole presence of DNA topoisomerase II. The band intensity increased in the presence of mAMSA, while no significant difference occurred in the cleavage pattern. The location of the cleavage sites along the c-myc locus revealed a striking correspondence with that of some DNase hypersensitive sites. These results indicate that DNA topoisomerase II is most certainly implicated in the mAMSA activity and that the drug stimulates the topoisomerase II cleaving activity at specific sites, which may be involved in the biological activity of the drug.

What is a T-cell clone? Effect of rIFN on T-cell clone function and T-cell receptor gene rearrangement

A T4+ proliferative, noncytotoxic cloned line acquires specific lytic function by treatment with recombinant interferon alpha or gamma. Simultaneous with the acquisition of this new cell function, a rearrangement of the T-cell receptor alpha gene occurs. These changes necessitate a revised concept of a T-cell clone regarding its T-cell receptor gene configuration and cell function.